1. Field of the Invention
The present invention relates to a method and apparatus for setting and changing parameters or functions of an implanted device such as a cardiac pacer and more particularly to an apparatus including a peizoelectric device which can be actuated to generate signals for setting and adjusting the implanted device at the will of the wearer or someone else, such as a medical technician.
2. Description of the Prior Art
Heretofore, it has been known to use piezoelectric elements in cardiac pacers such as for energizing a pacer as disclosed in U.S. Pat. No. 3,659,615 or U.S. Pat. No. 3,456,134 and to cause the pacer to vibrate in response to the wearer's activity in an attempt to automatically adjust the pacing rate to the wearer's physical activity, as disclosed in U.S. Pat. No. 4,140,132. Also it has been proposed to utilize a sensor in a pacing lead for sensing blood pressure as disclosed in copending U.S. patent application Ser. No. 632,625, filed July 19, 1985.
Also it has been suggested to use a special element, such as a magnet, for altering a pacing rate or to test the pacer, including its battery, in U.S. Pat. Nos. 4,304,238 and 4,312,354.
Further, it has been suggested to make such changes by use of an ultrasonic radiator operating on an implanted piezoelectric crystal in U.S. Pat. No. 3,777,762.
These prior art devices have generally used the special element (e.g., magnet or ultrasonic radiator) to react with a suitable implanted associate element (e.g., reed switch or piezoelectric crystal) and related circuitry to alter the pacing rate, albeit for increased or decreased pacing or testing. Unfortunately, the wearer may not want to use or will not have the special device, e.g., magnet, with him at all times so that he cannot alter his pacing rate when he wishes.
The automatic type devices, such as disclosed in U.S. Pat. No. 4,140,132 have the disadvantage of having mechanical parts which are less reliable than solid state electronics. Further, the automatic type devices could make rate changes when not desired or fail to make rate changes when desired. For example, assume that the automatic device is implanted in the upper part of the body of the user, near or with the other portions of the pacer. With such an installation, the device becomes sensitive to upper body movement, and is less sensitive to or insensitive to lower body movement. Were the user to bicycle, where there is a great deal of lower body or leg movement, but relatively little upper body movement, the automatic device may not be sensitive enough to cause the desired change in pacing rate to match the increased muscular activity. Were the automatic device's sensitivity increased to compensate, then there is a likelihood that other normal, upper body motions, such as when being bounced about in an automobile on a somewhat bumpy road, would also cause unwanted changes in pacing rate. Clearly, the so-called automatic devices have their drawbacks since it is difficult to make a mechanical automatic type device that will always provide the correct pacing rate. With the apparatus of the present invention one can activate or deactivate an automatic device when the wearer feels it appropriate to do so.